Systems and methods for opening of a tissue barrier in primates

ABSTRACT

Systems and methods for cavitation-guided opening of a targeted region of tissue within a primate skull are provided. In one example, a method includes delivering one or more microbubbles to proximate the targeted region, applying an ultrasound beam, using a transducer, through the skull of the primate to the targeted region to open the tissue, transcranially acquiring acoustic emissions produced from an interaction between the one or more microbubbles and the tissue, and determining a cavitation spectrum from the acquired acoustic emissions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/575,044, filed on Sep. 18, 2019, which is a continuation of U.S.patent application Ser. No. 14/091,010, filed on Nov. 26, 2013, which isa continuation-in-part of International Patent Application No.PCT/US2012/039708, filed on May 25, 2012, which claims priority to U.S.Provisional Application No. 61/490,440, filed on May 26, 2011, thedisclosure of each of which is incorporated by reference herein in itsentirety. This application is also related to U.S. patent applicationSer. No. 12/077,612, filed Mar. 19, 2008, International PatentApplication No. PCT/US2009/056565, filed Sep. 10, 2009, InternationalPatent Application No. PCT/US2010/049681, filed on Sep. 21, 2010, andU.S. patent application Ser. No. 13/426,400, filed on Mar. 21, 2012, thedisclosure of each of which is incorporated by reference herein in itsentirety.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH

This invention was made with government support under Grant Nos.R01AG038961, R01 EB009041 and R21 EY018505 awarded by the NationalInstitutes of Health and CAREER 0644713 and MH059244 awarded by theNational Science Foundation. The government has certain rights in theinvention.

BACKGROUND

Certain neurological disorders and neurodegenerative diseases, such asAlzheimer's disease and Parkinson's disease, can be difficult to treatdue at least in part to the impermeability of the blood-brain barrier(BBB). Mechanical stress induced by the activation of microbubbles in anacoustic field is one noninvasive technique to temporarily open the BBB,and can be performed without damaging the surrounding tissue. BBBopening with focused ultrasound (FUS) can be performed in some animals,including mice, rabbits, rats, and pigs. However, extending thistechnique to other species can be difficult due to differences inphysiology and anatomy.

A passive cavitation detector (PCD) can be used to transcraniallyacquire acoustic emissions from interaction between a microbubble andbrain tissue during BBB opening in mice. This manner of transcranialcavitation detection in other species, for example monkeys, can be moredifficult at least in part because the thickness and attenuation of amonkey skull can be as much as about 2.5 times higher than a murineskull. Thus, improved systems and techniques for opening of a tissuebarrier in primates, including systems and techniques for performing invivo transcranial and noninvasive cavitation detection are needed.

SUMMARY

Systems and methods for cavitation-guided opening of a tissue in aprimate are disclosed herein.

In one embodiment of the disclosed subject matter, methods forcavitation-guided opening of a targeted region of tissue within aprimate skull are provided. In an example embodiment, a method includesdelivering one or more microbubbles to proximate the targeted region,applying an ultrasound beam, using a transducer, through the skull ofthe primate to the targeted region to open the tissue, transcraniallyacquiring acoustic emissions produced from an interaction between theone or more microbubbles and the tissue, and determining a cavitationspectrum from the acquired acoustic emissions.

In some embodiments, the method can be performed in vivo. The method caninclude determining the distance between the skull and the transducerbased on the acoustic emissions, and the method can include determininga focal depth of the transducer based on the acoustic emissions.

In some embodiments, the method can include determining an obstructionof the opening of the tissue based on the cavitation spectrum, anddetermining the obstruction can include detecting a vessel between theultrasound beam and the targeted region or proximate to the targetedregion. The method can include adjusting the targeted region based onthe obstruction, and in some embodiments, the adjusting can includeadjusting the targeted region by avoiding the vessel or shielding by thevessel.

In some embodiments, the method can include determining the presence ofinertial cavitation during opening, and/or adjusting one or moreparameters to prevent the inertial cavitation. The one or moreparameters can be a size of the one or more microbubbles and/or anacoustic pressure of the ultrasound beam. Adjusting the one or moreparameters can include selecting the one or more microbubbles having asize within a range of between about 1 to 10 microns, or in someembodiments, between about 4 to 5 microns. Additionally oralternatively, adjusting the one or more parameters can includeadjusting the acoustic pressure of the ultrasound to be within a rangebetween about 0.10 to 0.45 MPa at the targeted region.

In another embodiment of the disclosed subject matter, systems for invivo, cavitation-guided opening of a targeted region of tissue within aprimate skull are provided. In an example embodiment, a system includesan introducer to deliver one or more microbubbles to proximate thetargeted region Such a system also includes a transducer, coupled to thetargeting assembly, to apply an ultrasound beam through the skull of theprimate to the targeted region to open the tissue, a cavitationdetector, adapted for coupling to the skull and for transcranialacquisition of acoustic emissions produced from an interaction betweenthe one or more microbubbles and the tissue, and a processor, coupled tothe cavitation detector, configured to determine a cavitation spectrumfrom the acquired acoustic emissions.

In some embodiments, the processor can be further configured todetermine the distance between the skull and the transducer based on theacoustic emissions. Additionally or alternatively, the processor can befurther configured to determine a focal depth of the transducer based onthe acoustic emissions.

In some embodiments, the processor can be further configured todetermine an obstruction of the opening of the tissue based on thecavitation spectrum. The obstruction can include a vessel between theultrasound beam and the targeted region and/or proximate to the targetedregion. The processor can be further configured to adjust the targetedregion based on the obstruction. Additionally or alternatively, theprocessor can be further configured to adjust the targeted region basedon the obstruction to avoid the vessel and/or shielding by the vessel.In some embodiments, the processor can be further configured todetermine the presence of inertial cavitation during opening, and adjustone or more parameters to prevent the inertial cavitation. The one ormore parameters can be a size of the one or more microbubbles and/or anacoustic pressure of the ultrasound beam. The size of the one or moremicrobubbles can be adjusted to within a range of between about 1 to 10microns, or in some embodiments, between about 4 to 5 microns. Theacoustic pressure can be adjusted to within a range between about 0.10to 0.45 MPa at the targeted region.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated and constitute part ofthis disclosure, illustrate some embodiments of the disclosed subjectmatter.

FIGS. 1a-1d are diagrams illustrating an exemplary system forcavitation-guided opening of a tissue in a primate in accordance with anexemplary embodiment of the disclosed subject matter.

FIGS. 2a-2c are diagrams illustrating an exemplary targeting method foruse with a method for cavitation-guided opening of a tissue in a primatein accordance with an exemplary embodiment of the disclosed subjectmatter.

FIG. 3 are images illustrating targeting regions in a brain forcavitation-guided opening of a tissue in a primate in accordance with anexemplary embodiment of the disclosed subject matter.

FIG. 4 is a diagram illustrating an exemplary method forcavitation-guided opening of a tissue in a primate in accordance with anexemplary embodiment of the disclosed subject matter.

FIGS. 5a-5f are images illustrating further features of the method ofFIG. 4.

FIGS. 6a-6c are images illustrating further features of the method ofFIG. 4.

FIGS. 7a-7j are images illustrating further features of the method ofFIG. 4.

FIGS. 8a-8f are images illustrating further features of the method ofFIG. 4.

FIG. 9 includes images illustrating further features of the method ofFIG. 4.

FIG. 10 includes images illustrating further features of the method ofFIG. 4.

FIG. 11 is a graph illustrating further features of the method of FIG.4.

FIG. 12 is a graph illustrating further features of the method of FIG.4.

FIG. 13 includes images illustrating further features of the method ofFIG. 4.

FIGS. 14a-14c are images illustrating further features of the method ofFIG. 4.

FIG. 15 is a diagram illustrating an exemplary system for in vitrocavitation-guided opening and monitoring of a tissue in a primate inaccordance with an exemplary embodiment of the disclosed subject matter.

FIGS. 16A-16D are diagrams illustrating exemplary results for in vitrocavitation monitoring according to the disclosed subject matter.

FIGS. 17A-17D are images illustrating exemplary results for in vitrocavitation monitoring according to the disclosed subject matter.

FIGS. 18A-18I are diagrams illustrating exemplary in vitro cavitationdoses according to the disclosed subject matter.

FIGS. 19A-19D are diagrams illustrating exemplary in vitro cavitationSNR according to the disclosed subject matter.

FIGS. 20A-20C are diagrams illustrating exemplary in vivo cavitationdoses using 100 and 5000 cycles according to the disclosed subjectmatter.

FIGS. 21A-21B are diagrams illustrating exemplary in vivo cavitation SNRaccording to the disclosed subject matter.

FIGS. 22A-22D are diagrams illustrating exemplary in vivo BBB opening at275 kPa, 350 kPa, 450 kPa and 600 kPa, respectively, according to thedisclosed subject matter.

FIGS. 23A-23D are images illustrating exemplary safety assessmentsaccording to the disclosed subject matter.

Throughout the figures and specification the same reference numerals areused to indicate similar features and/or structures.

DETAILED DESCRIPTION

The systems and methods described herein are useful for in vivotranscranial, noninvasive cavitation detection and opening of a tissuewith microbubbles and allow for real-time monitoring. Although thedescription provides as an example opening the blood-brain barrier(BBB), the systems and methods herein are useful for opening othertissues, such as muscular tissue, liver tissue or tumorous tissue, amongothers.

The subject matter disclosed herein include methods and systems forcavitation-guided opening of a tissue in a primate. Accordingly, thetechniques described herein make use of transcranially-acquired acousticemissions produced from an interaction between the one or moremicrobubbles and the tissue, and determine a cavitation spectrum fromthe acquired acoustic emissions. The cavitation spectrum can be used,for example, to determine an obstruction of the opening of the tissue,and/or to adjust targeting of the tissue to avoid the obstruction. Thus,the disclosed subject matter can be utilized to perform acavitation-guided BBB opening to improve monitoring of the target ofsonication.

FIGS. 1a-1d show an exemplary system for in vivo FUS-induced BBB openingaccording to the disclosed subject matter. FIG. 1d illustrates anexemplary embodiment of a system 100 for in vivo cavitation-guidedopening of a tissue in a primate according to the disclosed subjectmatter. A single-element, circular FUS transducer 102 which can have ahole in its center and be driven by a function generator 104 (forexample, obtained from Agilent Technologies, Palo Alto, Calif., USA)through a 50 dB power amplifier 106 (for example, obtained from ENIInc., Rochester, N.Y., USA). The FUS transducer 102 can be mounted on astandard monkey stereotaxic frame for improved positioning accuracy, asshown for example in FIGS. 2a-2c . As shown in FIG. 1d , the FUStransducer 102 can be further coupled to the scalp and/or skull of theprimate using a coupling medium, which can be for example a coupling gelas used in standard ultrasound imaging. The center frequency, focaldepth, outer radius and inner radius of the FUS transducer can be withina range of 200-900 kHz, 40-120 mm, 10-40 mm, and 5-12 mm, respectively,and in some embodiments can be 500 kHz, 90 mm, 30 mm, and 11.2 mm,respectively. A single-element PCD 108 (as embodied herein with a centerfrequency: 7.5 MHz, focal length: 60 mm, Olympus NDT, Waltham, Mass.,USA) can be configured through the center hole of the FUS transducer102. The FUS transducer 102 and the PCD 108 can be aligned so that theirfocal regions overlap within the confocal volume. The PCD 108 can beconnected to a digitizer 110 (for example, obtained from Gage AppliedTechnologies, Inc., Lachine, QC, Canada) through a 20 dB preamplifier(for example, model no. 5800 obtained from Olympus NDT, Waltham, Mass.,USA), and can be used to passively acquire acoustic emissions frommicrobubbles.

FIGS. 2a-2c illustrate an exemplary targeting system for in vivoFUS-induced BBB opening according to the disclosed subject matter. Asshown in FIG. 2a , a positioning rod indicating the position of thefocus (for example, 5 cm away from the edge of the transducer) can beused to target. In FIG. 2b , the positioning rod can be mounted on themanipulator to locate the origin of the stereotactic coordinates. InFIG. 2c , the origin of the stereotactic coordinates, which can beindicated by an engraved cross on a metal piece between ear-bars, can betargeted with the tip of the positioning rod.

An exemplary method according to the disclosed subject matter wasperformed on five male rhesus macaques over the course of 12 sessions (atotal of 25 sonications), with two different protocols (A and B)implemented as shown in Table 1 and described further below. Theacoustic parameters of each protocol, such as the pulse length (PL),pulse repetition frequency (PRF), microbubbles used, and peakrarefractional pressure (PRP) are provided. A corresponding targetingregion and number (#) denotes the number of sonications performed in aregion, such as the Visual Cortex (VC), Hippocampus (HC), Caudate (Ca),and Putamen (Pu). N denotes the number of monkeys. The correspondingtargeting regions are illustrated in FIG. 3, in horizontal, coronal andsagittal views of the brain.

As embodied herein and shown in Table 1, in some protocols, 4-5 μmmicrobubbles were utilized, which were manufactured in-house andsize-isolated using differential centrifugation. In some protocols,polydispersed Definity® microbubbles (from Lantheus Medical Imaging, MA,USA) were utilized. Sonication was performed after intravenous (IV)injection of 500 μL microbubbles for all monkeys.

TABLE 1 PRF PNP Targeting Protocol PL (Hz) microbubble (MPa) (#) N A 100 cycles 10 Definity ® 0.20 VC (1) 1 0.25 VC (1) 1 0.30 VC (1) 1 B5000 cycles 2 Definity ® 0.30 HC (3) 2 0.45 HC (3) 2 0.60 HC (1) 1 4-5μm 0.30 VC (2), 4 Ca (2), Pu (1) 0.45 VC (4), 4 Ca (1), HC (1) 0.60 VC(2), 1 HC (2)

An exemplary method according to the disclosed subject matter isillustrated in FIG. 4. Two exemplary targets at 0.30 MPa (indicated withthe dark circle) and 0.45 MPa (indicated with the light circle) are alsoillustrated. As described above, at 402, microbubbles can beintravenously injected into the monkey. At 404, FUS and passivecavitation detection are performed. As embodied herein, for applicationof the FUS, all animals were anesthetized with 2% isoflurane (carriergas: oxygen). The heart rate was held at approximately 120 beats perminute and the respiratory rate at around 60 breaths per minute. Priorto sonication, the scalp hair was removed with a depilatory cream toimprove acoustic transmission. The animal's head was then placed in astereotactic frame to facilitate targeting of the ultrasound. Thesonication was performed after intravenous (IV) injection of a 500-4,microbubble bolus in all experiments (5×10⁹ numbers/mL for customizedmicrobubbles and 1.2×10¹⁰ numbers/mL for Definity®). Targeting wasfurther improved using a manipulator and a positioning rod indicatingthe position of the focus relative to the stereotaxic coordinates (asshown in FIG. 2).

Magnetic resonance imaging (MRI) at 3.0 T (Philips Medical Systems,Andover, Mass., USA) was used to confirm and quantify the BBB openingfollowing the opening. Three-dimensional (3D) spoiled gradientT1-weighted sequences (TR/TE=20/1.4 ms; flip angle: 30°; NEX=2; spatialresolution: 500×500 μm; slice thickness: 1 mm with no interslice gap)were applied after intravenous (IV) injection of gadodiamide (fromOmniscan®, GE Healthcare, Princeton, N.J., USA) about 1 hour aftersonication. Gadodiamide presence in the brain parenchyma was induced bythe BBB opening. 3D T2-weighted sequence (TR/TE=3000/80; flip angle:90°; NEX=3; spatial resolution: 400×400 μm²; slice thickness: 2 mm withno interslice gap) and 3D Susceptibility-Weighted Image (SWI) sequencewere applied (TR/TE=19/27 ms; flip angle: 15°; NEX=1; spatialresolution: 400×400 μm²; slice thickness: 1 mm with no interslice gap)and were used to assess brain damage. In the session of closing timelineand accuracy, FSL, a library of analysis tools for MRI brain imagingdata, was used to perform the image registration to keep the brainorientation at the same location for the closing timeline determination,and the focal shift identification.

As discussed above, two exemplary protocols were implemented herein. Inprotocol A in Table 1, Definity® microbubbles were utilized withrelatively short PL (for example, 100 cycles) at 0.20-0.30 MPa. Theresults are illustrated in FIGS. 5a-5f . FIG. 5a shows a spectrogramwithout microbubble administration as a baseline. Spectrograms duringFUS sonication of a monkey at 0.20 MPa (FIG. 5b ), 0.25 MPa (FIG. 5c )and 0.30 MPa (FIG. 5d ), and magnetic resonance (MR) images with coronal(FIG. 5e ) and sagittal planes (FIG. 5f ) are also shown. FIGS. 5a-5fillustrate that no BBB opening was induced with protocol A, for examplein the region indicated with the dashed circle, although inertialcavitation, i.e., broadband response, was shown in each case. Thus,microbubble response was detected through the monkey skull.

In protocol B in Table 1, relatively long PL (for example, 5000 cycles)and higher pressure (0.30-0.60 MPa) were applied with Definity® or4-5-μm diameter bubbles. FIG. 6a shows a spectrogram without microbubbleadministration as a baseline. FIG. 6b shows a spectrogram during FUSsonication of a monkey at 0.45 MPa and indicates a broadband response.FIG. 6c shows an MR image of the sagittal plane, and indicates that noBBB opening was induced, for example in the region of the dashed circle.Thus, as shown in FIG. 6, no BBB opening was induced at 0.45 MPa usingDefinity®, but a broadband response was detected.

In protocol B using the 4-5-μm microbubbles, however, the BBB was openedat 0.30 and 0.45 MPa. FIG. 7a is the baseline image showing no higherharmonics or broadband response present. The spectrogram correspondingto the first pulse with microbubbles administered shows that broadbandacoustic emissions, i.e., inertial cavitation, are detected at 0.30 MPa(FIG. 7b ) and 0.45 MPa (FIG. 7c ). The white arrow in FIG. 7c indicatesthat the time-point of occurrence of the second harmonic coincides withthe travel distance to the skull. Therefore, harmonics higher than the3rd harmonic and any broadband response in FIGS. 7b and 7c can beconsidered to be due to microbubble effects. MR images in FIGS. 7d-7hconfirm opening of the BBB. Deposition of the MRI contrast agent in thebrain tissue after ultrasound exposure detected in the MR imagesindicate that the BBB was opened at 0.30 MPa (shown in FIGS. 7d, 7e, and7g ) and 0.45 MPa (shown in FIGS. 7f and 7h ) using the 4-5-μm bubbles.At least the white matter can be observed to be opened in FIGS. 7d-7h inthe circled region. The peak MR intensity enhancement at the BBB-openedregion relative to the average value in the parenchyma was increased by119% and 48% at 0.3 MPa and 0.45 MPa, respectively. The volume of theBBB disruption was 24.6 mm³ and 30.5 mm³, respectively. The two distinctopened sites were separated by a distance of 4.74 mm.

The spectrograms obtained during treatment can also provide targetingguidance. The different time of flight for each harmonic can allow thedepth at which different phenomena occurs to be determined. For example,FIG. 7i shows the spectrogram of FIG. 7c , providing the depthcorresponding to the time of flight for each harmonic. In FIG. 7i ,bubble activity at the focus and non-linear effects induced by the skull(as indicated by the white arrow) can be distinguished. As such, bubbleactivity can be measured to occur about 4.5 cm below the skull, which isin agreement with the initial MR-atlas planning.

The skull can be used as a reference point to quantify the depth of thetransducer focus. Due to the amount of pressure applied duringtreatment, certain non-linear effects induced by the bone interface arenot necessarily detected during sonication. To avoid this, the pressurecan be increased during the control acquisition until the appearance ofthe second harmonic (as shown in FIG. 7j ). The pressure can be safelyincreased because, at this point of the procedure, bubbles generally arenot present in the system. Thus, based on the acoustic emissions shownin FIG. 7j , the skull depth can be determined, and the result candisplayed, for example on a real-time PCD monitoring, to providetreatment guidance.

The MRI sequence described above and an IV contrast agent injection wererepeated six days after BBB opening. No intensity enhancement wasobserved indicating that the BBB was closed or reinstated. T2-weightedand susceptibility-weighted MRI sequences were used to assess potentialbrain damage after ME-FUS. FIGS. 8a, 8c and 8d show the 3D T2-weightedsequence. FIGS. 8b, 8e and 8f show susceptibility-weighted image (SWI)sequence. The sonicated regions are highlighted in dashed circles. Noedemas or hemorrhages can be seen in the sonicated regions. The sameprotocol described above was repeated for the two following sessionsapplying 0.6 MPa and two different kinds of microbubbles. The resultsare shown in FIGS. 9 and 10. FIG. 9 shows images from sonicationperformed using the Definity® microbubbles and applying 0.6 MPa to thetargeted region (indicated by the dashed circles). The 3D SpoiledGradient-Echo (SPGR) T1-weighted sequence was applied after intravenousinjection of gadodiamide about 1 hour after sonication. No damage isshown in the T2-weighted sequence. FIG. 10 shows images from sonicationperformed using the customized microbubbles and applying 0.6 MPa to thetargeted region (indicated by the dashed circles). The 3D SPGRT1-weighted sequence was applied after intravenous injection ofgadodiamide about 1 hour after sonication. An edema is indicated in theT2-weighted sequence.

The T1-weighted MR sequences were used to track the diffusion ofgadodiamide. The peak MR intensity enhancement at the BBB-opened regionrelative to the average value in the parenchyma was increased by 68% and41% using the customized and Definity® microbubbles, respectively. Thevolume of the BBB disruption was equal to 285.5 mm³ and 116.3 mm³,respectively. The BBB opening regions at the caudate and the hippocampuswere shifted from the targeted location by respectively 0.6 mm and 0.9mm laterally and 6.5 mm and 7.2 mm axially. T2-weighted MR sequenceswere also used to assess potential damage in the brain. An edematousregion was detected on the T2-weighted MRI in one case using thecustom-made microbubbles while no damage was detected using Definity®with the same acoustic parameters. A subsequent qualitative assessmentof basic animal behavior has been performed. Normal cognitive behaviorhas been noted following ME-FUS procedures at moderate pressures andusing Definity®. In the case of the 0.6 MPa application of thecustomized microbubbles, the animal showing the edema exhibited aweakness in the contra-lateral arm over four days after treatment, butthen showed a recovery after the four days. The correspondingspectrogram showed that a large broadband signal was recorded for boththe customized and Definity® microbubbles.

As shown in Table 1, a total of 11 BBB openings were induced at 0.30 and0.45 MPa using 4-5-μm diameter bubbles. A correlation between theinertial cavitation dose (ICD) and the BBB opening volume is shown inFIG. 11. At 0.60 MPa, because the BBB opening volume was due to thecombination of four sonications (two in the visual cortex and two in thehippocampus), this opening volume (285.5 mm3) is not included in FIG.11. The stable cavitation dose (SCD) at all ultra-harmonics ofdifference regions at 0.30 and 0.45 MPa is shown in FIG. 12. At 0.30MPa, the amplitude at ultra-harmonics was the largest in the putamen andthe lowest in the visual cortex. At 0.45 MPa, the amplitude in thevisual cortex was higher than in the caudate and the hippocampus.

The duration of BBB opening and the corresponding opening volume of eachscan are illustrated in FIG. 13. BBB opening was performed in a monkeycaudate using 0.30 MPa and 4-5 μm microbubbles. The highlighted regionin the images illustrates the opening region, which is no longer visiblein day 4. The corresponding quantification of BBB opening volume in thegraph indicates that the BBB is nearly closed on day 2. The error barillustrates the standard deviation of the MR intensity of the BBBopening area. Thus, at 0.30 MPa, the BBB was opened in the caudate, andthe opening was reinstated after two days. On day 4, the opened BBB wascompletely recovered. The targeting precision was also investigated. Anaxial shift of the focus was found to be about 3.4 mm for the Caudateregion and about 6.9 mm for the Visual Cortex region. The correspondingspectrograms over the 2 min duration are also shown. The focal shift,BBB opening volume, and MM contrast enhancement of the visual cortex andcaudate are quantified in Table 2.

TABLE 2 Region Caudate Visual cortex Pressure (MPa) 0.30 0.45 Axialfocal shift (mm) 3.4 6.9 Volume (mm³) 72.5 112.3 MR Enhancement 52% 63%

Accordingly, FUS-induced BBB opening, along with transcranial cavitationdetection, in non-human primates is provided according to an embodimentof the disclosed subject matter. As discussed above with respect toTable 1, sonication in four locations were performed in five animalsaccording to the embodiments discussed herein. Pressures ranging from0.3 MPa to 0.6 MPa were utilized. Increased pressure can result in alarger BBB opening extent and higher BBB permeability, while a “safetywindow” can be considered to be within the pressure range of 0.30 MPaand 0.60 MPa. In the exemplary embodiments, T1-weighted MRI at 3.0 T wasused to confirm the results of the disclosed subject matter, confirmingBBB disruption by tracking the diffusion of IV-injected gadodiamide inthe brain. The cavitation response can be used to estimate the BBBopening volume and predict the occurrence of BBB opening.

To illustrate the effectiveness and determine further applications ofthe disclosed subject matter, the results of BBB opening in primatesaccording to the disclosed subject matter can be compared to knownmethods for opening the BBB in other animals, such as mice. In theembodiments herein, except for the case of sonication performed at 0.60MPa, no BBB opening was induced using Definity® microbubbles and 10-mspulse length, despite the occurrence of inertial cavitation (as shownand described with respect to FIGS. 5 and 6). Accordingly, relativelylower pressures (for example, 0.20-0.30 MPa) and shorter pulse length(for example, 0.2 ms) utilized in protocol A can be ineffective toinduce BBB opening. However, using techniques for BBB opening in mice,the BBB was opened at 0.45 MPa and PLs of 0.1, 0.2, 1, 2, and 10 ms,using comparable microbubbles. Thus, relatively higher pressures (forexample, 0.30-0.60 MPa) can be necessary to open the BBB in monkeysusing Definity®.

Further, the medial areas were targeted as shown in FIG. 5, and thus thefocus included the superior sagittal sinus that, due to the relativelylarge volume of microbubbles circulating, resulted in larger amplitudeof the cavitation spectrum. Measuring the cavitation spectrum can,therefore, be utilized to determine whether a large vessel is in thepath of the FUS beam, and thus predict or avoid its effects on inducingBBB opening. The exact location of the focus in the brain can bedifficult to predict, and further, the exact location of large vesselsin the brain relative to the beam is generally not known in advance.Hence, the relationship between the amplitude of the cavitationspectrum, the area of BBB opening, and the BBB opening threshold canprovide useful additional information regarding the presence of largevessels close to the focus. This information can thus be used to predictwhether opening of the BBB is obstructed due to the focal spot proximityto a large vessel resulting in subsequent shielding and/or adjust thetargeting accordingly to achieve BBB opening, i.e., by avoidingshielding by large vessels.

The results according to the disclosed subject matter can also beutilized to determine the dependence of the BBB opening on themicrobubble types. In protocol B, at 0.30 and 0.45 MPa, BBB opening wasonly observed with the 4-5 μm bubbles, as illustrated in FIGS. 7 and 8.At 0.60 MPa, a larger BBB opening area was obtained with the 4-5 μmbubbles, as illustrated in FIGS. 9 and 10. This can be due, at least inpart, to a larger portion of the brain reaching the disruption thresholdwhen peak pressure increases. The 4-5 μm bubbles can result in a largerBBB opening region in mice. Thus, the results disclosed herein are inqualitative agreement that the bubble size can affect the BBB opening inprimates according to the disclosed subject matter.

The BBB can be opened at 0.3 MPa and inertial cavitation can occur at0.45 MPa using 1.5-MHz FUS and 4-5 μm diameter bubbles. In theembodiments described herein, the BBB was also opened at 0.30, 0.45, and0.60 MPa with the presence of inertial cavitation. The mechanical indexwas 0.25, 0.37, and 0.49 at 1.5 MHz, as well as 0.42, 0.64 and 1.02 at500 kHz for 0.3 MPa, 0.45 MPa and 0.6 MPa, respectively. The MIthreshold of the broadband response was about 0.451 and the broadbandresponse was observed in most cases of BBB opening, and thus lowerpressures can be applied and the stable cavitation dose can bequantified to determine whether the BBB can be opened with stablecavitation, and without inertial cavitation, using 4-5-μm diameterbubbles, and thus avoid the potential for damage to the subject that canbe caused by inertial cavitation.

The cavitation response can be utilized to estimate the BBB openingvolume. Statistical analysis of cavitation responses during BBB openingin mice indicates that the ICDs and BBB opening volume can be bothpressure and bubble-size dependent. Regression analysis shows a linearcorrelation can occur between the ICD and the BBB opening volume atvarious bubble diameters. Thus, by analyzing the 11 openings performedwith the 4-5-μm bubbles as embodied herein, volume prediction using theICD can be performed, for example as illustrated in FIG. 11. In oneembodiment of the disclosed subject matter, BBB opening can be performedand the corresponding opening volume can be predicted using the PCDsystem without the use of MRI for monitoring BBB opening duringsonication. In this manner, FUS according to the disclosed subjectmatter can be applied while further reducing costs and improvingreal-time capability in clinical applications.

From the cavitation response, in addition to the ICD, the spectrogramcan be used to analyze microbubble behavior in real-time. In FIG. 14a ,a spectrogram of total duration (i.e., 120 seconds or 2 minutes)indicate the duration for microbubbles to reach the brain after theIV-injection. For example, FIG. 14a shows a duration of 10 seconds forDefinity® microbubbles to reach the brain. Thus, the spectrogram oftotal duration can be used, for example in a clinical application, toidentify if a patient has a circulation problem affecting the movementof the microbubbles. The persistence of the microbubbles can also beidentified.

In FIG. 14b , the spectrogram of one pulse (identified with the verticalline in FIG. 14a ), shows a pulse length of 10 ms, and can be utilizedto determine the duration of inertial cavitation. The duration can bemicrobubble dependent and correlated to the ICD. If insufficientmicrobubbles are sonicated at each pulse, the duration of inertialcavitation can be shorter such that lower ICD and BBB opening volume areinduced.

In FIG. 14c , the first few hundred microseconds of one pulse(identified with the box in FIG. 14b ), are shown and can indicate thelocation of the focus based on the starting point of harmonics andbroadband response. This spectrogram can be utilized to estimate theactual focus, and thus determine the axial shift between the actualfocus and the desired targeting region.

Since the primate brain is generally inhomogeneous, the BBB openingproperties can be distinct among different areas of the brain. As shownfor example in FIG. 7, the intensities of MRI contrast enhancement inthe BBB opening region at 0.30 MPa was 2.3 times higher than at 0.45MPa. These differences can be due, at least in part, to a higherconcentration of microbubbles in the sonicated region during the 0.30MPa stimulation such than MRI contrast is enhanced and the broadbandresponse is stronger.

Likewise, the cavitation response can also be region dependent. Asdiscussed above, the SCD at distinct regions at 0.30 and 0.45 MPa isshown in FIG. 11. The relatively higher sensitivity is shown near thecenter frequency of the PCD (i.e., at about 7.5 MHz). Four differentlocations were shown, each having a distinct cavitation response. Forexample, as shown in FIG. 11, at 0.30 MPa, the amplitude level islargest in the putamen and smallest in the visual cortex. Further,comparing the caudate shown in FIG. 12 and the visual cortex shown inFIG. 13, the visual cortex is deeper than the caudate such that loweramplitudes are detected in the visual cortex. A comparison between thecaudate and putamen can be made from FIG. 3. As shown, the putamen isdeeper than caudate in the sagittal view, but is roughly the same depthin the coronal view. Further sonications can be performed in the putamento determine the region dependent cavitation response. A furthercomparison between the visual cortex and hippocampus can be made fromFIG. 3. As shown, the hippocampus is deeper than visual cortex from thesagittal and coronal view such that the amplitude detected was lower inthe hippocampus. Although the depth of the targeting regions can affectthe PCD amplitude, the region dependent cavitation can furthercharacterize the BBB opening properties in different locations inprimates.

Accordingly, noninvasive and transcranial cavitation detection duringBBB opening in nonhuman primates are provided herein. Further, the MRIcontrast enhancement and cavitation response can be considered to beregion and/or microbubble-size dependent. Inertial cavitation can failto induce BBB opening, for example when the focus overlaps with largevessels such as the superior sagittal sinus, and thus the systems andmethods according to the disclosed subject matter can be utilized toperform a cavitation-guided BBB opening to improve monitoring of thetarget of sonication.

According to another aspect of the disclosed subject matter, FUS-inducedBBB opening can be performed in vitro in macaque and human primateskulls. Furthermore, skull effects and real-time monitoring ofFUS-induced BBB opening of primate skulls can be performed in vivo.

At least three types of cavitation doses and cavitation SNR can bequantified and used to address the characteristics of cavitation, skullattenuation, and detection limit. The stable cavitation dose (SCD)representing the overall extent of stable cavitation can be representedas the cumulative harmonic or ultraharmonic emission. The inertialcavitation dose (ICD) can represent the overall extent of inertialcavitation, and can be represented as the cumulative broadband acousticemission. The cavitation SNR can be represented as the ratio of post- topre-microbubble administration cavitation doses.

FIG. 15 shows an exemplary system 1500 for in vitro FUS-induced BBBopening according to the disclosed subject matter. With reference toFIG. 15, system 1500 can include a single-element FUS transducer 1502(for example and as embodied herein, H-107, Sonic Concepts, WA, USA),which can be operated at 0.5 MHz with a −6-dB focal width by lengthequals to 5.85 mm by 34 mm and a geometric focal depth of 62.6 mm forsonication. A spherically focused, flatband hydrophone 1504 (for exampleand as embodied herein, Y-107, Sonic Concepts, WA, USA; −6-dBsensitivity: 10 kHz-15 MHz) can be coaxially and confocally aligned withthe transducer 1502 and can be utilized as the passive cavitationdetector. For example, and as embodied herein, a PC work station 1506(for example and as embodied herein, model T7600, Dell) with MATLAB®(Mathworks, MA, USA) can be configured and utilized to automaticallycontrol the sonication through a function generator 1508 (for exampleand as embodied herein, model 33220A, Agilent Technologies, CA, USA)followed by a 50-dB amplifier 1510 (for example and as embodied herein,A075, ENI, NY, USA). An exemplary controller to control the sonicationthrough the function generator 1508 can be implemented using theexemplary computer program module in the Computer Program ListingAppendix hereto. PCD signal acquisition can be performed using a 14-bitanalog-to-digital converter 1512 (for example and as embodied herein,Gage Applied Technologies, QC, Canada, at sampling rate: 100 MHz and 50MHz in vitro and in vivo, respectively). A 20-dB amplification can beapplied during opening of the macaque skull, for example usingpreamplifier 1514. By comparison, 10 dB can be applied usingpreamplifier 1514 for the human skull, which can be suitable due atleast in part to increased reflection in the human skull. PCD signals invivo, including the frequency spectra and cavitation doses can bemonitored in real time as described herein.

In one embodiment, a desiccated macaque skull can be provided and can besectioned to retain the cranial part (including, for example, frontalbone, parietal bones, and occipital bone), as shown for example in FIG.15. The averaged thickness of the skull in the ultrasound beam path can3.09 mm using a caliper at five points of the skull lined in a crossbelow the transducer 1502, and can be degassed for 24 hours prior to BBBopening.

In an alternative embodiment, a desiccated human skull can be providedand can be sectioned to retain the frontal and the parietal bones, asshown for example in FIG. 15, with an averaged thickness of 4.65 mmusing the same measuring method described above. The human skull can bedegassed for 48 hours prior to BBB opening. The pressures at the focusof the FUS transducer with and without the skulls can be calibratedusing bullet hydrophone 1504.

A number of sonications can be performed, as summarized in Table 3.In-house, lipid-shell, monodisperse microbubbles (for example, embodiedherein having median diameter: 4-5 μm) can be diluted to 2×105bubbles/mL and injected to the 4-mm-in-diameter channel in theacrylamide phantom before and after placing the skull. The channel canbe approximately 45 mm and 25 mm below the macaque and the human skull,respectively. The PCD with the hydrophone and the diagnostic B-modeimaging system (as embodied herein from Terason, MA, USA) can be used,separately or in combination, to monitor the sonication (for example andas embodied herein having peak negative pressure (PNP): 50-450 kPa,pulse length: 100 cycles (0.2 ms) and 5000 cycles (10 ms), pulserepetition frequency (PRF): 10 Hz, duration: 2 s), and thus can beconfigured to avoid interference with the PCD. B-mode images of bubbledisruption can be acquired to support the FUS focusing at the channel,which can be performed through a linear array transducer (for exampleand embodied herein as 10L5, Terason, MA, USA; having center frequency:5.1 MHz) and can be placed transversely to the FUS beam.

TABLE 3 Number of in vitro sonications. Without With microbubblesmicrobubbles Skull effect Macaque No skull 41 49 (100 cycles) Skull 3346 Human No skull 60 60 Skull 70 81 Pulse length effect No skull 20 20(5000 cycles)

The in vitro system can be configured to mimic the in vivo conditionsfor targeting through the skull. For example and as embodied herein, FUScan be applied through the parietal bone proximate the sagittal suture,which can correspond to the position for targeting the thalamus,putamen, and caudate nucleus. Additionally or alternatively, the 4-mmchannel can be utilized to accommodate the area of bubble disruption atthe increased pressure (for example, 450 kPa). The reduced microbubbleconcentration can be utilized at least in part to reduce or minimize thebubble-bubble interaction (for example providing a mean distance betweenbubbles of 58.5 mm) while still capable of being captured for B-modevisualization. The sonication parameters (for example, pulse length,PRF, duration) can be set at described herein, which can modify thedetection threshold. Sonication using 5000-cycle pulses without theskull in place can be performed in accordance with the in vivotechniques described herein.

In exemplary embodiments, in vivo FUS-inducement and BBB openingtechniques can be performed. In one example, in vivo skull effects fromFUS-inducement can be examined. In another example, BBB opening inprimates can be performed. For each example, a number of sonicationsperformed is summarized in Table 4. In each example, microbubbles wereintravenously injected, and the total number of microbubblesadministered was calculated based on the subject's weight. For purposeof illustration, and as embodied herein, for BBB opening a bolus ofmicrobubbles (for example, 2.5×10⁸ bubbles/kg) was injected and thesonication (for example, PNP: 250-600 kPa, pulse length: 10 ms, PRF: 2Hz, duration: 2 min) started at the beginning of injection. For purposeof illustration, and as embodied herein, for examining the in vivo skulleffect, a bolus of microbubbles (for example, 1.25×10⁸ bubbles/kg) wereinjected after the BBB opening sonication. Ten seconds after theinjection, the microbubbles perfused to the brain, and a consecutivesonication at ramp-up pressures was started (for example, PNP: 50-700kPa, pulse length: 100 cycles (0.2 ms) or 5000 cycles (10 ms), PRF: 2Hz, duration: 10 s). The thalamus and putamen were targeted as describedherein.

TABLE 4 Number of in vivo sonications. Pulse Without With lengthmicrobubbles microbubbles Skull effect  100 cycles 8* 8* 5000 cycles14** 14** BBB opening 5000 cycles 40  40  *6 at 700 kPa. **12 at 700kPa.

For example, and as embodied herein, Magnetic Resonance Imaging (forexample, using 3T, Philips Medical Systems, MA, USA) was performedone-half hour after the sonication to confirm BBB opening and assesssafety. Spoiled Gradient-Echo T1-weighted sequence (for example,TR/TE=20/1.4 ms; flip angle=30°; NEX=2; spatial resolution: 500×500 μm²,slice thickness: 1 mm with no interslice gap) before and 40 min afterintravenously injecting the contrast agent gadodiamide (for example,Omniscan®, GE Healthcare, NJ, USA; dosage: 0.2 mL/kg), was used tovisualize the opening, as described further herein. T2-weighted sequence(for example, TR/TE=3000/80 ms; flip angle=90°; NEX=3; spatialresolution: 400×400 μm², slice thickness: 2 mm with no interslice gap)was performed for detecting edema. Susceptibility-weighted imaging (forexample, SWI, TR/TE=19/27 ms; flip angle=15°; NEX=1; spatial resolution:400×400 μm², slice thickness: 1 mm with no interslice gap) was performedfor detecting hemorrhage.

Analysis for the opening volume across the targeted regions includedimage re-alignment, enhancement evaluation, and volume calculation. Thepre-contrast and post-contrast images were aligned to the individualstereotactically aligned T1-weighted images acquired using FSL's FLIRTprogram to determine suitable alignment of the pre- to post-contrastimages. The ratio of the post- to the pre-contrast images were taken andnormalized by setting 0 and 1 to the mean of the contralateral regionopposed to the sonicated region (for example, and as embodied herein, acircle of 6.25 mm in diameter in the horizontal slice) and the anteriorcerebral artery (for example, and as embodied herein, a circle of 1.75mm in diameter in the horizontal slice), respectively, and the openingregion was thresholded by three times standard deviation of thecontralateral (unsonicated) region. The volume was the accumulatedvoxels over the threshold in the sonicated region times the voxel size.

The PCD signals, frequency spectra, and spectrograms (for example, andas embodied herein, using an 8-cycle Chebyshev window, 98% overlap,4096-point Fast Fourier Transform) were used to monitor the cavitationusing MATLAB®. The cavitation level-time derivative of the cavitationdose can be quantified, and as such the harmonic, ultraharmonic, and thebroadband signals in the spectra for each pulse can be separatelyfiltered. The stable cavitation level based on harmonics only (dSCD_(h))can be represented as the root-mean squared amplitude of the harmonicsignals in a single pulse, with the harmonic signals represented as themaxima in the 20-kHz (−6-dB width) range around the harmonic frequency(0.5 f*n) in the frequency spectrum. The stable cavitation level basedon ultraharmonics only (dSCD_(u)) can be represented as the root-meansquared amplitude of the ultraharmonic signals in a single pulse, withthe ultraharmonic signals represented as the maxima in 20 kHz around theultraharmonic frequency (0.5 f*n+0.25f) in the frequency spectrum. Theinertial cavitation level (dICD) can be represented as the root-meansquared amplitude of the frequency spectrum after excluding theharmonics (360 kHz around the harmonic frequency) and ultraharmonics(100 kHz around the ultraharmonic frequency).

The cavitation dose for each sonication can be represented as thecumulative sum of the cavitation level in 1.25-5.00 MHz for every pulse;the cavitation SNR, can be represented as the ratio of post- topre-microbubble administration cavitation doses.

Cavitation dose(CD)=Σ_(t=0-T)dCD_(t)=Σ_(t=0-T)√{square root over ( S ²)}_(t)

Cavitation SNR=20 log(CD_(post)/CD_(pre))  (1)

where t can represent the time for each pulse; T can represent thesonication duration; CD can represent the cavitation dose (SCD_(h),SCD_(n), and ICD for harmonics, ultraharmonics, and broadband emissions,respectively); dCD_(t) can represent the cavitation level for the pulseat time t (dSCD_(h), dSCD_(u), and dICD for harmonics, ultraharmonics,and broadband emissions, respectively); √{square root over (S² )}_(t)can represent the root-mean squared amplitude of theharmonic/ultraharmonic/broadband signals in the frequency spectrum forthe pulse at time t; CD_(post) can represent the post-microbubbleadministration cavitation dose; CD_(pre), can represent thepre-microbubble administration cavitation dose.

For purpose of illustration, and as embodied herein, the frequency rangeused to quantify the cavitation level can be 1.25-5.00 MHz, which can besuitable to cover the strong harmonics, ultraharmonics, and broadbandemission, while suppressing the linear and nonlinear scattering from thetissue and the skull. The quantification of the SCD_(h) and the SCD_(u)can be based on the acoustic emissions generated by the stablecavitation, including harmonics and ultraharmonics. The harmonics andultraharmonics can be quantified separately due to the large differenceof the spectral amplitudes. Such physical mechanisms can be consideredto be different: the harmonics can be the result of volumetricoscillation, while the ultraharmonics and subharmonics can relate to thenonspherical bubble oscillation. Regarding quantifying the ICD, thewidth of the spectral window for the broadband signals can be chosen toreduce or minimize both the electronic noise and the increase due atleast in part to the harmonic peaks. That is, the window width can belarge enough to reduce or minimize the electronic noise by averaging andto not cover the broadening part of harmonic peaks.

The SCD based on subharmonics (SCD_(s)) can be excluded due at least inpart to the intrinsic low-frequency noise. The excitation frequency usedcan be relatively low, and as such the subharmonics can be overlappingwith the linear scattering, whose amplitude can increase further withthe scattering of the skull.

For purpose of illustration and not limitation, and as embodied herein,in the in vitro technique, an unpaired two-tailed Student's t-test canbe used to determine if the treatment (post-microbubble administration)was significantly higher than the control (pre-microbubbleadministration) for each pressure. Additionally or alternatively, in thein vivo skull effect analysis, a paired two-tailed Student's t-test canbe used to determine if the treatment (post-microbubble administration)was significantly higher than the control (pre-microbubbleadministration) for each pressure in each subject. The results of theexemplary statistical analysis is described further herein.

FIGS. 16A-16D illustrate the PCD spectrograms before and after placingthe skull. Before placing the skull, the amplitude of harmonics,ultraharmonics as well as the broadband signals increased significantlywith pressure after microbubble administration, as shown for example inFIG. 16B with comparison to the control of FIG. 16A, in which the secondharmonic became significant at and above 150 kPa. The broadband signalsincreased mostly within the range of 3-5 MHz according to the results at150 kPa and 200 kPa in FIG. 16B. After placing the macaque skull, asshown for example in FIG. 16C, the high frequency components wereattenuated, while the signals remained detectable at the lowest pressure(for example, 50 kPa). After placing the human skull, as shown forexample in FIG. 16D, the frequency components below 3 MHz were detectedat and above 100 kPa.

For purpose of illustration and not limitation, and as embodied herein,B-mode cine-loops were also used to monitor the cavitation separately.FIGS. 17A-17D illustrate the images of the microbubbles in the channelphantom after sonication. The microbubbles were found to collapse at andabove 200 kPa evidenced by the loss of echogenicity in the focal regionin cases without the skull, as shown for example in FIG. 17A, with themacaque skull, as shown for example in FIG. 17B, with the human skull,as shown for example in FIG. 17C, and using longer pulses without theskull (for example, 5000 cycles as shown in FIG. 17D. The mean diameterof the hypoechogenic area at 200 kPa and 450 kPa was 1.3 mm and 4 mm,respectively.

FIGS. 18A-18I illustrate cavitation doses with and without the skull inplace using 100-cycle pulses. Using the macaque skull, as shown forexample in FIGS. 18A-18C, the SCD_(h), the SCD_(u), and the ICD,respectively, without placing the skull, were significantly higher(p<0.05) than the control at and above 50 kPa, which also increasedmonotonically with pressure. After placing the macaque skull, theSCD_(h) was detectable (p<0.05) at all pressures, whereas the detectionpressure threshold for both the SCD_(u) and the ICD increased to 150kPa. Using the human skull, as shown for example in FIGS. 18D-18F, theSCD_(h) was detectable at and above 100 kPa after placing the skull. Forthe SCD_(u), the detection pressure threshold increased to 250 kPa. Forthe ICD, the detection pressure threshold became 350 kPa. The SCD_(h) atand above 400 kPa was undetected at least in part because the controlsignal with the human skull was strong. While the detection pressurethreshold slightly changed after placing the macaque and the humanskull, the sensitivity of cavitation doses to pressure changes remainedthe same.

The pulse length effect on the cavitation dose was also analyzed. FIGS.18G-18I illustrate the cavitation doses with 100-cycles and 5000-cyclepulse lengths. The SCD_(h) using 100-cycle pulses increasedmonotonically with pressure increase, whereas the SCD_(h) with5000-cycle pulses reached a maximum at 300 kPa and started to decreaseat pressures above 300 kPa. Similar to the SCD_(h), the SCD_(u) using100-cycle pulses increased monotonically with pressure, while theSCD_(u) using 5000-cycle pulses reached a plateau at 250 kPa and startedto decrease at higher pressures. The ICD using 100-cycle and 5000-cyclepulses both increased monotonically with pressure increase, and thelatter increased at a faster rate. As shown, the cavitation doses of5000-cycle pulses were higher than that of 100-cycle pulses.

FIGS. 19A-19D illustrate the cavitation SNR, which can be used toanalyze the sensitivity of PCD using pulse lengths, the detection limit,and skull attenuation. Before placing the skull, as shown for example inFIG. 19A, the cavitation SNR for the SCD_(h), SCD_(u), and ICD using100-cycle pulses ranged within 28.6-49.1 dB, 2.1-38.9 dB, and 3.1-37.0dB, respectively. As shown, followed by the SCD_(u) and the ICD, thecavitation SNR for the SCD_(h) was the highest. The cavitation SNR forthe SCD_(h), SCD_(u), and ICD using 5000-cycle pulses, as shown forexample in FIG. 19B, ranged within 24.8-54.6 dB, 2.2-54.8 dB, and2.9-41.9 dB, respectively. Both the cavitation SNR for the SCD_(h),SCD_(u) reached a plateau at 250 kPa, while the cavitation SNR increasedmonotonically for the ICD.

FIGS. 19C-19D show the cavitation SNR using 100-cycle pulses through theskull. The cavitation SNR through the macaque skull, as shown forexample in FIG. 19C, corresponded to the statistically significantSCD_(h), SCD_(u), and ICD through the macaque skull, as shown forexample in FIGS. 18A-18C, and ranged within 9.7-29.4 dB, 1.6-15.6 dB,and 1.1-14.1 dB, respectively. The cavitation SNR through the humanskull, as shown for example in FIG. 19D, corresponded to thestatistically significant SCD_(h), SCD_(u), and ICD through the humanskull, as shown for example in FIGS. 18D-18F, and ranged within 2.4-6.2dB, 1.4-3.0 dB, and 1.2-1.9 dB, respectively. For the cavitation SNRwith the skull lower than 1 dB, the corresponding cavitation doses wereshown to not reach statistical significance. As such, the PCD signalswere suitable for analysis when the cavitation SNR exceeded 1 dB.

As described herein, the cavitation SNR with the skull, as shown forexample in FIGS. 19C-19D can be correlated to the cavitation doses withthe skull, as shown for example in FIGS. 18A-18F. As shown, when thecavitation SNR exceeded 1 dB, the transcranially acquired cavitationdoses were statistically significant. The skull attenuation can beassessed. For example and as embodied herein, the cavitation SNR withoutthe skull, as shown for example in FIG. 19A, can be compared with thecases with the skull surpassing the 1-dB SNR limit, as shown for examplein FIGS. 19C-19D. As shown, the SNR without the skull was above 15.2 dBand 34.1 dB to be detected through the macaque and the human skull,respectively. The skull attenuation can be calculated by dividing by theskull thickness: for example and as embodied herein, 4.92 dB/mm and 7.33dB/mm for the macaque and human, respectively.

For example, and as embodied herein, in vivo skull effects at differentpressures and different pulse lengths were analyzed and compared withthe results of the in vitro techniques. FIGS. 20A-20C illustrate thecavitation doses using 100- and 5000-cycle pulses. When applying100-cycle pulses, as shown for example in FIGS. 20A-20C, the SCD_(h),SCD_(u), and ICD, respectively, were significantly higher than thecontrol at and/or above 300 kPa, 700 kPa, and 600 kPa, respectively.Furthermore, when applying 5000-cycle pulses, the SCD_(h), SCD_(u), andICD were significant at pressure lower than that for the 100-cyclepulses: at and above 100 kPa, at 200 kPa and 700 kPa, and at and above250 kPa, respectively. The cavitation dose when applying 5000-cyclepulses was higher than that with 100-cycle pulses. In either case, thecavitation doses increased monotonically with pressure increase.Besides, the SCD_(h) using 100-cycle pulses at 450 kPa, the SCD_(h)using 5000-cycle pulses at 150 kPa, and the ICD using 5000-cycle pulsesat 300 kPa showed no significance (0.05<p<0.06) due to their highervariability.

FIGS. 21A-21B illustrate the cavitation SNR for the skull effect using100- and 5000-cycle pulses. When applying 100-cycle pulses, as shown forexample in FIG. 21A, the cavitation SNR for the statisticallysignificant SCD_(h), SCD_(u), and ICD ranged within 1.2-9.8 dB, 2.3 dB,and 0.7-2.1 dB, respectively. As shown, the cavitation SNR increasedmonotonically for the SCD_(h) and ICD, and fluctuated for the SCD_(u).When applying 5000-cycle pulses, as shown for example in FIG. 21B, thecavitation SNR for the SCD_(h), SCD_(u), and ICD ranged within 3.8-13.3dB, 1.4-3.5 dB, and 1.0-6.1 dB, respectively. As shown, the cavitationSNR reached a plateau for the SCD_(h) at 250 kPa and started to decreaseat 400 kPa. For the SCD_(h), the cavitation SNR fluctuated at lowpressures and increased monotonically at and above 400 kPa. For the ICD,the cavitation SNR increased monotonically without fluctuating orreaching a plateau. The cavitation SNRs for pressures where significantcavitation signals were detected were all above the 1-dB SNR limit, withan exception for SCD_(u), in which 57% of the measurements passing thedetection limit were statistically insignificant. Such results wereconsistent with the corresponding in vitro results.

Realtime PCD monitoring during BBB opening is illustrated hereinaccording to the disclosed subject matter. FIGS. 22A-22D each illustrateone of four examples, respectively, of PCD monitoring and thecorresponding opening results in MRI at different pressures. The MMshowed BBB opening in two macaques in the thalamus and the putamen atpressures ranging from 250 kPa to 600 kPa, with opening volumes of338.6, 223.8, 213.4, and 262.5 mm³, respectively. The volume increasedwith pressures in the same macaque, as shown for example in FIGS.22B-22D, in general, and the volume range varied among subjects. ThedSCD_(h) reached a plateau in 10-30 seconds after injecting microbubblesand was kept at the same level for the rest of sonication duration. ThedSCD_(u) remained mostly undetected. The dICD increased by 3.18 dB at350 kPa and 0.19 dB at 450 kPa as compared the end of the sonication tothe beginning, while it remained unchanged at 275 kPa and 600 kPa.

FIGS. 23A-23D illustrate the safety assessment using T2-weighted MRI andSWI corresponding to the four BBB opening cases in FIGS. 22A-22D. Ineach example, no edema or hemorrhage was detected, which corresponded tothe PCD monitoring results for which minimum or no ICD increase was seenduring sonication.

For purpose of illustration, and as embodied herein, the sensitivity,reliability, and the transcranial cavitation detection limit in macaquesand humans were investigated, using both in vitro macaque and humanskull techniques as well as in vivo techniques for the skull effect andBBB opening in macaques as described herein. The in vitro techniquesallowed for precise control to investigate cavitation characteristicsand the skull effects, while the in vivo techniques confirmed the invitro findings using realtime PCD monitoring. The transcranial PCD wasfound sensitive to detect cavitation signals at pressures as low as 50kPa. The transcranial detection limit (for example and as embodiedherein as 1-dB SNR limit) served as a criterion to determine reliabledetection. Realtime PCD monitoring was performed during BBB opening, inwhich safe opening and reliable detection was achieved using longpulses.

B-mode imaging was used to visualize the cavitation, to achieve suitablefocal alignment to the channel and the pressure in situ. B-mode imagingvisualized cavitation by the maintenance or loss of echogenicity,representing stable or inertial cavitation, respectively. B-mode imagingalso confirmed suitable focal alignment to the channel before and afterplacing the skull by detecting the bubble collapse at the center of thechannel. Furthermore, suitable pressure in the channel was achievedafter placing the skull at least in part because the loss ofechogenicity became detectable at 200 kPa.

In contrast to the active visualization of B-mode imaging, the PCDserved as an indirect monitoring tool. The PCD was shown to be moresensitive than B-mode imaging at least in part because it detectedinertial cavitation at 50 kPa, lower than the lowest pressure losingechogenicity (e.g., 200 kPa). Detecting bubble destruction in B-modeimaging can be inhibited by its spatial and contrast resolution, whichgenerally did not detect a smaller amount of bubble destruction atpressures lower than 200 kPa. As such, B-mode imaging was used tosupplement to the PCD results rather than to determine the inertialcavitation threshold. As shown, the inertial cavitation occurred at 50kPa as described herein, due at least in part to low excitationfrequency, long pulse lengths, and low stiffness of the in-housemicrobubbles with a 4-5 μm diameter.

For purpose of illustration and not limitation, with reference to FIGS.18A-18I, the pulse length was shown to affect the characteristics of thecavitation doses. Using 100-cycle pulses, the cavitation doses increasedmonotonically with pressure increase as the magnitude of bubbleoscillation increased. Furthermore, using long pulses (e.g., 5000cycles) was found to be more effective in generating higher cavitationdoses. In this manner, the ICD still increased monotonically withpressure increase, while the SCD_(h) and the SCD_(u) reached a plateauat 250 kPa. As such, under a long-pulse excitation, a larger number ofmicrobubbles underwent stable and inertial cavitation, and stablecavitation reached a plateau and started to decrease when mostmicrobubbles were undergoing inertial cavitation and collapseimmediately without contributing to stable cavitation. Furthermore, themicrobubbles undergoing stable cavitation diffused faster using longerpulses and failed to enhance the SCD_(h).

With continued reference to FIGS. 18A-18I, through the skull the changeof cavitation doses to pressure change remained the same, while thepressure threshold for the cavitation doses becoming detectable varieddepending on the type of cavitation doses and the skull. The monotonicalincrease of cavitation doses to pressure increase remained the sameafter placing the macaque and the human skull for signals surpassed theskull attenuation. By comparison, the pressure threshold to detect theSCD_(h) through the macaque skull was unchanged, while it increased forthe SCD_(h) and ICD; for the human skull, the threshold increased forthe three types of cavitation doses. For each type of cavitation doses,the pressure threshold for the SCD_(h) was the lowest, followed by theSCD_(u) and ICD. The SCD_(h) remained detectable through the skull at 50kPa and 100 kPa for macaques and humans, respectively. For the SCD_(u)and ICD, the pressure threshold increased to 150 kPa and 350 kPa formacaques and human respectively due at least in part to low signalintensity, while the ultraharmonics and the broadband emissions occurredat 50 kPa.

Referring now to FIGS. 20A-20C, the in vivo skull effect was supportedby the in vitro results, except that the in vivo SCD_(u) was lessreliable. Using 100-cycle and 5000-cycle pulses, the SCD_(h) as well asthe ICD increased monotonically with pressure as in the in vitro cases,with the exception that the SCD_(h) for the 5000-cycle pulse did notreach a plateau, which can be due at least in part to the nonlinearscattering from the skull and air trapped between the transducer and thesubject's skin. By comparison, the SCD_(u) can be less reliable due atleast in part to the less frequent ultraharmonics and can be attributedto the biological environment such as blood, capillary, and bloodvessel. Furthermore, the varying blood pressure can contribute tovariation the SCD_(u). Additionally, the inertial cavitation wasdetected at and above 250 kPa, although microbubble collapse can occurat lower pressures.

For purpose of illustration and not limitation, and as embodied herein,the cavitation SNR was defined and used to investigate the sensitivityand reliability of PCD under different conditions, such as variedpressures and pulse lengths, and the skull effects thereon. Suchtechniques can provide a quantitative way to find the transcranialdetection limit (for example, embodied herein as a 1-dB SNR limit), theskull attenuation, as well as techniques to improve the detection. Toachieve improved PCD, the cavitation SNR can be increased, for exampleand without limitation, by increasing the pressure, the pulse length,and/or the number of microbubbles injected. As shown herein, usinglonger pulse lengths (e.g., 5000 cycles) was effective in increasing thecavitation SNR at low pressures (e.g., less than 250 kPa, while thecavitation SNR for the SCD_(h) decreased at high pressures (e.g., above250 kPa) due at least in part to the cavitation characteristics andnonlinear skull scattering. Increasing the number of microbubblesinjected can also improve the cavitation SNR, at least in part becausethe inertial cavitation can be detected at lower pressures (e.g., 250kPa) in the in vivo skull effect analysis techniques after a secondbolus injection of microbubbles.

The cavitation signals were considered reliable through the skull with acavitation SNR above 1 dB. That is, the signals were strong enough tosurpass skull attenuation. The 1-dB SNR level was determined using thein vitro technique and confirmed using the in vivo technique. Using eachtechnique, the cavitation doses showed statistical significance whensatisfying this criterion with the only exception in SCD_(u). In thismanner, the transcranial detection level provides an indication ofinertial cavitation detected using the macaque subjects. Furthermore,such a determination can provide an indication of reliable PCD for alltypes of cavitation doses.

The skull attenuation for macaque was measured as 4.92 dB/mm and forhuman was measured as 7.33 dB/mm. As such, the attenuation by the humanskull is higher than that for macaque, which can be due to at least inpart to increased skull density, increased nonlinear ultrasoundtransmission, increased reflections and different extents of modeconversion. The cavitation SNR can be increased to surpass the 1-dB SNRlevel by increasing the pressure, the pulse length, and/or the number ofmicrobubbles injected as discussed above. Furthermore, the in situcavitation strength can be determined by combining the transcranial PCDmeasurements (for example, above the 1-dB SNR level) with the skullattenuation acquiring from simulation and/or ex vivo measurement toassess the treatment outcome.

Additionally, the inherent skull attenuation, nonlinear ultrasoundscattering due at least in part to the skull can inhibit or prevent thedetection of harmonics. As shown for example in FIG. 18D, nonlinearscattering from the human skull can become apparent at and above 450kPa, inhibiting or preventing the detection of the harmonics (SCD_(h))generated by the microbubble cavitation. Such a result can be due atleast in part to higher pressure applied to compensate for the 80% ofpressure attenuation through the human skull, which can introducenonlinear scattering. Furthermore, as embodied herein, the FUS focus was25 mm below the human skull, which can introduce increased nonlineareffects compared to deeper focus. In addition, trapped air can bepresent, which can inhibit or prevent detection. As shown for example inFIG. 20A, such a result occurred in the in vivo macaque results, inwhich nonlinear scattering was introduced using a 5000-cycle pulse. Suchnonlinear effects can thus inhibit or prevent the detection of theSCD_(h) and can lead to overtreatment due at least in part to themonitoring.

Additionally, and as embodied herein, realtime monitoring of thecavitation doses was performed during BBB opening using 5000-cyclepulses, providing information related to bubble perfusion and thecavitation level. Furthermore, and as embodied herein, the use of suchlong pulses can provide reliable PCD monitoring and facilitate openingat low pressures. The SCD_(h) can be monitored as described herein, andthe time for microbubbles perfuse to the sonicated region as well as themicrobubble persistence during the entire treatment can be monitored atpressures as low as 250 kPa. The ICD can be monitored as describedherein, and the safety of the treatment can be assumed in real time atleast in part because low or no inertial cavitation was detected in theexamples of safe BBB opening. Low or no ICD obtained during BBB openingexperiments, as shown for example in FIGS. 22A-22D, compared to the invivo skull effect analysis, as shown for example in FIGS. 20A-20C, canbe due at least in part to lower numbers of microbubbles circulatingduring BBB opening, at least in part because an increase of ICD wasobtained in the same subject after a second bolus injection ofmicrobubbles during the in vivo skull effect analysis.

As shown for example in FIGS. 22A-22D, safe BBB opening was achieved atlow pressures (e.g., 250-600 kPa) in both the putamen and the thalamus.No differences were observed in the putamen and the thalamus in terms ofcavitation doses or opening threshold in this study. The opening volumevaried across subjects, but increased with pressure in the same macaque,as illustrated by comparison of the 350-kPa example shown in FIG. 22Bwith the 600-kPa example shown in FIG. 22D. The 450-kPa example shown inFIG. 22C had smaller opening volume than the 350-kPa example, asindicated at least in part by the slightly decreasing SCD_(h), which canbe due at least in part to the subject's physiological effect to thecirculating microbubbles. Furthermore, the average SCD_(h) at differentpressures was at the same level, owing to the cavitation characteristicsusing long pulses and the high variation between examples, as shown forexample in FIGS. 20A-20C.

Correlating the cavitation doses to the opening volume based onsingle-element PCD can be performed using the ICD instead of theSCD_(h). This can be performed at least in part because the positivecorrelation of the ICD to pressure can be independent of the pulselength, which can affect the cavitation characteristics. Additionally,the ICD typically is not affected by the nonlinear ultrasound scatteringdue to the skull (as illustrated for example by the human skull resultsin FIGS. 18D-18F). Furthermore, the ICD can also provide a safetyassessment, as described herein. Reliable ICD detection can be achievedby increasing the cavitation SNR. In addition, passive cavitationmapping, including spatial information of cavitation can provide moreprecise estimation of opening volume and safety assessment using boththe SCD_(h) and ICD.

For purpose of illustration, and as described herein, in vitro macaqueand human skull techniques as well as in vivo macaque techniques toanalyze the skull effect and BBB opening are provided. As shown, throughthe macaque skull the pressure threshold for detecting the SCD_(h)remained the same, while it increased for the SCD_(u) and ICD. Throughthe human skull, the pressure threshold increased for each type ofcavitation dose. The pressure threshold for detection the SCD_(h) wasthe lowest, followed by the SCD_(u) and ICD. The change of cavitationdoses to pressure increase remained the same through the skull where thesignal intensity surpassed the skull attenuation (for example, and asembodied herein 4.92 dB/mm for the macaque and 7.33 dB/mm for thehuman). The transcranial PCD was found to be suitable when thecavitation SNR exceeded the 1-dB SNR level in both in vitro and in vivoexamples. Using long pulses can allow for reliable PCD monitoring andfacilitates BBB opening at low pressures. The in vivo resultsillustrated that the SCD_(h) was detected at pressures as low as 100kPa; the ICD, at 250 kPa and can occur at lower pressures; the SCD_(u),at 700 kPa and was less reliable at lower pressures. Realtime monitoringof PCD was performed in vivo in macaques during BBB opening, and safeopening has been achieved at 250-600 kPa in both the thalamus and theputamen, with minimum or no inertial cavitation detected. Furthermore,transcranial PCD in macaques in vitro and in vivo as well as humans invitro can be considered reliable, for example by improving thecavitation SNR to surpass the 1-dB detection level.

We claim:
 1. A system for opening of a targeted region of tissue,comprising: an introducer to deliver one or more microbubbles to aregion of tissue proximate to the targeted region; a transducer, coupledto a targeting assembly, to apply an ultrasound beam to the targetedregion to open the tissue; a cavitation detector, adapted foracquisition of acoustic emissions produced from an interaction betweenthe one or more microbubbles and the tissue; and a processor, coupled tothe cavitation detector, configured to: determine a cavitation spectrumfrom the acquired acoustic emissions; determine whether a vessel islocated between the ultrasound beam and the targeted region or proximateto the targeted region based on the cavitation spectrum; and anddetermine a cavitation signal-to-noise ratio (SNR) from the acquiredacoustic emissions, wherein the cavitation SNR is a ratio of post- topre-microbubble cavitation doses.
 2. The system of claim 1, wherein theprocessor is further configured to determine a distance between thetissue and the transducer based on the acoustic emissions.
 3. The systemof claim 1, wherein the processor is further configured to determine afocal depth of the transducer based on the acoustic emissions.
 4. Thesystem of claim 1, wherein the processor is further configured todetermine an obstruction of the opening of the tissue based on thecavitation spectrum.
 5. The system of claim 4, wherein the processor isfurther configured to adjust the targeted region based on theobstruction.
 6. The system of claim 5, wherein the processor is furtherconfigured to adjust the targeted region based on the obstruction toavoid the vessel or shielding by the vessel.
 7. The system of claim 1,wherein the processor is further configured to determine a presence ofinertial cavitation during opening, and adjust one or more parameters toprevent the inertial cavitation.
 8. The system of claim 7, wherein theone or more parameters is selected from the group consisting of a sizeof the one or more microbubbles and an acoustic pressure of theultrasound beam.
 9. The system of claim 8, wherein the size of the oneor more microbubbles is adjusted to within a range of between 1 to 10microns.
 10. The system of claim 8, wherein the acoustic pressure isadjusted to within a range between 0.3 to 0.45 MPa at the targetedregion.